1. Field of the Invention
The present invention relates to a fluorescent lamp apparatus for providing light and, more particularly, to a fluorescent lamp having a convoluted envelope, and a lamp apparatus which incorporates this fluorescent lamp and can be used, for example, as a direct replacement of incandescent lamps.
2. Problems of the Prior Art
The conventional fluorescent lamp apparatus of the type described above comprises a fluorescent lamp having a convoluted envelope forming a discharge passage, a base member having a base of the same type as that of the ordinary incandescent lamp and supporting the fluorescent lamp, a globe attached to the base member and enclosing the fluorescent lamp, and a lighting circuit provided within the base member. The lighting circuit necessarily has ballast, e.g., a choke coil, for limiting the amount of current flowing through the circuit. The choke coil generates heat for as long as the fluorescent lamp is turned on, as do the lamp electrodes. Since the lamp is attached to the base structure containing the choke coil and has a convoluted envelope, it is heated to a higher temperature than a straight tubular type lamp.
Generally, the luminosity of a fluorescent lamp depends upon the ambient temperature. When the temperature of the mercury vapor source of the fluorescent lamp rises above the upper limit of the optimum temperature range, the luminosity of the lamp drops. A fluorescett lamp apparatus of the type which is free of this problem is disclosed in Japanese Utility Model Application Disclosure No. 59-28956. This apparatus comprises a base containing a lighting circuit, and a globe section including a convoluted fluorescent lamp. The base section and the globe section are detachably connected, and an air gap is provided between them. This air gap is open to the atmosphere, and cool air is always in this gap. The air gap, therefore, reduces the transfer of the heat generated from the lighting circuit to the fluorescent lamp in the globe section. The mercury vapor source of the lamp is not heated above the upper limit of the optimum temperature range, and the a drop of the luminosity of the lamp is prevented.
Japanese Patent Disclosure No. 60-207241 discloses a fluorescent lamp apparatus wherein a quantity of amalgam is contained within a convoluted envelope. More specifically, the amalgam mass is provided in an exhaust tube protruding from that portion of the envelope in which stems having electrodes are located. The use of the amalgam mass as a mercury vapor source, raises the upper limit of the optimum temperature range, whereby a drop of the luminosity, which may result from a temperature rise of the envelope, can be more readily prevented.
Attempts have been made to develop fluorescent lamp apparatuses which are smaller and provide a greater output than those described above. The lamp of each of these apparatuses generate much heat. Even if an air gap is provided in the lamp apparatus, thus reducing the transfer of heat from the lighting circuit to the lamp, the mercury vapor source of this lamp is heated to a temperature above the upper limit of the optimum range. A mass of amalgam may be contained in the lamp in order to raise the upper limit of the optimum temperature range. Even so, the luminosity of the lamp apparatus may drop.